Use a UV/haze filter when you are shooting late in the day and want to cut UV/Haze. Other than that, it's just another layer of glass to distort your photos and adversely affect image quality.

To protect the front element of the lens, install a (flower-)petal style lens hood, and leave it there. No need for a lens cap with that on, while mounted to the camera at least, and the hood will improve image-quality with no downside.

I use UV/haze filters as protective elements only in two cases: the front element of my ultra-wide 10-22mm lens is bulbous and rather exposed, and the hood is too big round to leave on in the bag -- so there often is a filter attached to that lens.

The second scenario is my very expensive f2.8 70-200mm-IS lens, which again won't fit into the bag with hood attached. The front element of that beast is (I believe) synthetic flourite, and very VERY expensive to replace.

For any modestly priced lens, I wouldn't bother.

Most modern plastic zooms let a ton of dust/dirt in through the zoom mechanism, so adding a filter to the end won't help significantly with that, either.

Cheers